Résumé dans la langue de publication, traduction non disponible A variable capacity viscous heater whose capacity is reliably decreased and whose heating efficiency does not lower even after a long term use. Formed are, for example, a recovery passage (3a) communicating with the central area of a heating chamber (10) and capable of being opened and closed, a supply passage (3c) communicating with the lower portion of the heating chamber (10), and a control chamber (CR) communicating with the recovery passage (3a) and the supply passage (3c). Silicone oil in the heating chamber (10) is recovered by use of the Weissenberg effect into the control chamber (CR) through the recovery passage (3a), which is open, to decrease the capacity. Silicone oil in the control chamber (CR) is fed into the heating chamber (10) through the supply passage (3c) to increase the capacity.